This invention relates to a process for the manufacture of silyl ketene acetals. More specifically, this invention relates to a means for producing bis(silyl)ketene acetals (BSKA) having the formula, EQU (CH.sub.3)RC.dbd.C(OSiR.sup.i.sub.3).sub.2,
from the reaction of a trisubstituted silane and an allyl 2-organoacrylate having the formula, ##STR1## R is selected from a group consisting of alkyl groups, aryl groups, alkaryl groups, and substituted alkyl, aryl, and alkaryl groups. R.sup.i is independently selected and is selected from a group consisting of alkyl groups, aryl groups, alkaryl groups, substituted alkyl, aryl, and alkaryl groups, alkoxy groups, halogen atoms, and organosiloxy groups.
The first reference to preparation of silyl ketene acetals (SKA) was in the late-1950's by Petrov et al., J. Gen. Chem. (USSR), 29(1959), pp. 2896-2899. This reference and most of the other references to the art deal with chemical species of the general formula, ##STR2## v has a value of 1 or more. Z is such groups as alkyl, alkenyl, aryl, alkaryl; any of these groups containing one or more functional groups, such as ether oxygen atoms, thio groups, organosiloxy groups, which are unreactive under silylating conditions.
Silyl ketene acetals are useful intermediates to prepare organic compounds which are difficult to synthesize by other means. Another recent application is the use of the SKA as acrylate polymerization initiators. This concept known as Group Transfer Polymerization (GTP) was developed by DuPont and is disclosed in three U.S. patents--U.S. Pat. No. 4,414,372, Farnham et al., issued Nov. 8, 1983; U.S. Pat. No. 4,417,034, Webster, issued Nov. 22, 1983; and U.S. Pat. No. 4,508,880, Webster, issued Apr. 2, 1985.
Four procedures for preparing silyl ketene acetals are known in the art. The first general route to SKA is the reaction of an ester of a carboxylic acid with an appropriate metal reagent to form a metal enolate ion and subsequent reaction of the enolate ion with an organochlorosilane. Ainsworth et al., J. Organometallic Chem., 46 (1972), pp. 59-71, describe the preparation of an SKA via the reaction of esters of carboxylic acids with lithium diisopropylamide, followed by reaction with trimethylchlorosilane. Kita et al., Tetrahedron Letters, 24: 12 (1983), pp. 1273-1276, discloses a similar procedure to prepare bifunctional SKA. Brown, J. Org. Chem., 39: 9 (1974), pp. 1324-1325, describes the preparation of metal enolate ions by reacting potassium hydride in tetrahydrofuran with a carbonyl compound, followed by reaction with excess triethylamine and trimethylchorosilane.
Kuo et al., Chemical Communications, (1971), pp. 136-137, discloses the preparation of bis(silyl)ketene acetals of the formula, EQU R.sup.1 R.sup.2 C.dbd.C[OSi(CH.sub.3).sub.3 ].sub.2,
wherein R.sup.1 and R.sup.2 are hydrogen, methyl, t-butyl, and phenyl. The silyl ketene acetal is prepared by the reaction of the corresponding carboxylic acid or silyl ester of a carboxylic acid in contact with lithium diisopropylamide, trimethylchlorosilane, and tetrahydrofuran.
In a second general procedure, silyl ketene acetals are prepared by the hydrosilation of esters of carboxylic acid with organohydrosilanes. Petrov et al., J. Gen. Chem. (USSR), 29 (1959), pp. 2896-2899, described the platinum-catalyzed reaction of methyl methacrylate with triethylsilane. Ojima et al., J. Organometallic Chem., 111 (1976), pp. 43-60, studied the use of tris(triphenylphosphine)rhodium chloride as a catalyst. Howe et al., J. Organometallic Chem., 208 (1981), pp. 401-406, and Yoshii et al., Chem. Pharm. Bull., 22 (1974), pp. 2767-2769, describe yields of 70-75% SKA from the reaction of (C.sub.2 H.sub.5).sub.3 SiH and methyl methacrylate using organophosphorous complexes of rhodium as a catalyst. Quirk et al., in European Patent Application No. 0184692, published June 18, 1986, discloses o-silylated ketene acetals and enol ethers and a process for their preparation from the reaction of acrylate esters and silanes or siloxanes in the presence of a rhodium catalyst.
In a third procedure Ishikawa et al., U.S. Pat. No. 4,482,729, issued Nov. 13, 1984, describes the preparation of a fluoroalkyl silyl ketene acetal by the reaction of a fluorinated carboxylic acid ester with trimethylsilyl trifluoromethanesulfonate.
The fourth procedure involves the alkali metal reduction of disubstituted malonates in the presence of trimethylchlorosilane to produce a silyl ketene acetal. Kuo et al., Chemical Communications, (1971), pp. 136-137; and J. Am. Chem. Soc., 94: 11 (1972), pp. 4037-4038, disclose the preparation of silyl ketene acetals of the formula, EQU R.sup.1 R.sup.2 C.dbd.C(OR.sup.3)OSi(CH.sub.3).sub.3,
from the reaction of a dialkyl dialkylmalonate with trimethylchlorosilane in the presence of sodium metal. R.sup.1, R.sup.2, and R.sup.3 are alkyl, aryl, or alkaryl groups.
It has now been discovered that bis(silyl)ketene acetals can be prepared by the reaction of a trisubstituted silane and an allyl 2-organoacrylate.